Now that the dispatcher does its own TryExecute, filters do not need to
do that. This change requires all worklets called by filters to be able
to execute without knowing the device a priori.
This will make it easier to support integrators as an ExecObject.
One side effect is that the integrators and partical advection
are not templated by the type of the field.
Regardless of the type of the field, there is probably little reason to
compute particle advection with less than 64 bit floats to account for
accumulated errors. This will make it easier to use these classes.
CMake 3.12 introduces a ...<max> syntax in the version given to
cmake_minimum_required to automatically set policies to NEW up
to that version. Use it to avoid listing policies explicitly.
